Film pulldown method



P 1952 E. w. KELLOGG ET AL 2,612,075

' FILM PULLDOWN METHOD Filed June 24, 1949 3 Sheets-Sheet l INVENTOR Eownna WKELLOGG ems/v P.

AORNEY Sept. 30, 1952 E. w. KELLOGG ET-AL FILM PULLDOWN METHOD Filed June 24, 1949 3 Sheets-Sheet 2 v 10 P v I" J; 6 i

1211 1; I 9 K I Sept. 30, 1952 Filed June 24, 1949 E. W. KELLOGG ET AL FILM PULLDOWN METHOD 3 Sheets-Sheet 3 ATTORNEY Patented Sept. 30, 1952 2,612,075 FILM PULLDOWN METHOD Edward w. Kellogg, Haddonfield, and WarrenR. Isom, West Collingswood, N. J., assignors to- Radio Corporation of America, a corporation of V Delaware Application June 24, 1949, Serial No. 101,042

13 Claims. (Cl. 88-18.4)

This invention relates to motion picture film advancing methods, and particularly to a claw intermittent drive of the cam and follower type.

This. application is related to U. S. Patent No. 2,484,348 of October 11, 1949, which discloses and claims the mechanism.

In a widely used form, the mechanism comprises 'a claw having one or more teeth to engage perforations in the, film, carried on an arm which is "pivoted at the end opposite to the claw, and actuated by a cam which is located at an intermediate point. This arrangement makes it possible to adjust the total "movement or throw of the claw by altering the ratio of the distances from pivot to claw. and from pivot to cam. Such an adjustment is very advantageous from a manufacturing standpoint, in that cams may, vary slightly in production, but it is important that the throw of the claw be held within-very close limits, the desired throw being greater than the film perforation pitch by a very small margin. The claw teeth must be positioned in line with the perforations, and with the ordinary type of pivot, this requirement precludes adjusting throw by shifting the pivot. An alternative is to shift the cam. This can be done, but atthe cost of considerable complication of mechanism. .Another alternative is to make the arm in two or more parts which can be fastened together'in altered relation, thereby for example altering the arm-length to compensate for moving the pivot. The present invention employs a novel form of pivot which permits moving the pivot point without disturbing the alignment of the claw teeth with respect to the film perforations.

In-the present invention, the above results are afiorded by a simple cam and follower mechanism easy to adjust and maintain in working condition while being economical to manufacture. The pivot-of the pull-down mechanism of the invention requires no lubrication and has 'no lost motion, and can be shifted to increase or decrease the throw without altering the lateral position of the claw with respect to the film in the picture gate. Neither is it necessary to'attach any adjusting device to the claw arm as in some known mechanisms.

A feature which is common to intermittent pull-down mechanisms is that -the'pull-down pins or teeth enter the perforations above the bottom edges of the perforations. No movement of 'the'filmoccurs until'the claw has begun-its downward'movement'and closed "up the gaps bringing the'contact surfaces of the pins against the edges of the film. Providing a throw adjustment-makes it possible to set this initial clearance at the smallest practicable value.

Furthermore, in the present invention, the cam is so shapedthat this preliminary movement is .at low velocity,.thereby preventing a sharp blow being struck against the film when the rapid portion of. the stroke begins. Also, the pull-down motionissuch that immediately after the rapid portion of the stroke, the pull-down pins are slightly displaced downwardly and then immediately back'to their .lower rest position at which the withdrawal ,of the pins begins. This motion pushes the .fi-lm slightly beyond the point at which .its rapid speed was stopped, thus taking up any ,variations which the powerful inertia effects may have introduced, while the slight rise ofthe pins causes them to clear the film before the withdrawal, and thus, avoid disturbing the film or wearing the film edges. These characteristics of the claw motion make it practicable to accomplish the pull-down in a minimum of timewithout random variations in the picture position on the one hand, one

cessive noise and wear on the film on the other hand. i p

The principal object of our invention, there fore, is to provide 'an improved cam and follower film pull-down action, which provides .a rapid pull-down with film safety. 1 Another object of the invention is to pro'vild improved accuracv-.-in the intermittent positioning of motionpicture .film in a camera or projection aperture.

. Another object of the invention is to provide an improved method of intermittently advance ing film to provide a, short pull-down time period and a comparatively long stationary time peri d.

A still further object .of the invention is sa evide a cam and follower film pull-down action having animproved motion .during the pull-down portion of the'cycle.

Although the novel features which are believed .to' be characteristic of this invention will he pointed out with particularity in the appended claims, the manner of its organization and the mode of its operation'will be better understood 19y referring t0 the win description. read In conjunction w h I he accompanyin draw,- ings, ing-a partjhereof, i which: I

Fig. '1 is aplan view of a pull-down mechanism embodying the invention.

'Fig. '2 is an elevational view of the invention as shown in il 'ig. -1. i----" Fig. 3 is a partial enlarged view in elevation of the invention'taken along-the line 3-3 of Fig. -1.

Fig. 4 is a detailed view of the throw adjustment taken along the line 4-4 of Fig. 2.

' Fig. 5 is a partial view in cross-section of -the 3 in-and-out and pull-down cams taken along the line 55 of Fig. 2, and

Figs. 6, 7, and 8 are diagrammatic views showing the principles of operation of one form of the invention.

Referringnow tojFigs, 6, '7, and8, a cam arm 5, having a follower 6,;is raised and lowered by-a cam 8 driven by a shaft 9. The'cam arm 5 has a claw H] at one .end and is mounted on a pair of fiat springs H and i2 at the other end, the springs being suitably stiffened by bending up the edges thereof, as shown at M and I5, respectively. The spring 'I l has one end fixedly attached on a mounting'jblock IT, while the spring l2 has one end mounted in an adjustable mounting block [8. A spring 28 maintains the follower 6 in contact'with the cam 8 at all times.

in line with their axes from executing any movements parallel to their average axes di-- rections, is approximate only. Actually, slightparallel movements would occur, but these are H is again anchored in the block H and the The two mounting springs H and 12 of Fig.6 V

produce the effectof a pivot, at A. Spring i4 will not permit any horisontalflmovement of the point A, and; spring '15 will not permit ,fany vertical movement thereof; but, by flexing, the springs will permit rotational motionabout the point The effective pivot is at the point of intersection of the axes of the two springs I16 and [5. If thetwo mounting blocks I] and-l3 are maintained'in fixed relative positions, the olevic'e of'Fig'." 6 would be equivalent to the conventional pivoted claw arm. The pivot point wouldiremain atjA, and thus, at a fixed distance from 'theclawlll. The pivot could be moved by movingboth' blocks together, just as a conventional pivot could be'm'oved, up or down, to bring the picture into frame, or to left or right to position the teeth with respect to the row of film perforations; 'bllt, such movement would alter the throw,"onconversely, if they arepositionedto give" thec'orrect throw, the claw position would probably be wrong. Hence, with conventional pivotsyitlis' usual to position the arm by correctlylocating the pivotin the horizontal direction, while it may be moved vertically to frame' the picturexil'Ihenfto adjust throw, it is necessary to movethejpoint of contact between cam 8 and follower-surface '5 to right or left. If,- on the other hand, the relative positionsof blocks-ti and I8 are altered, as shown in Fig.7, the effective pivotpoint can be moved,

for example, to the point 33, thereby altering the throw, without upsetting the claw position, and it is not necessary tofdoanythingto the cam and follower. The' eifect is equivalent to moving ap nventiOnalpiVQt to a new position on]: the frame of the machinefa'nd simultaneously moving it tonanewlposition on the claw arm,

such that the throw has lbeen, altered, but the lateral position of the arm has remained unchanged.

Assuming that itis desiredto' decrease the throw of theclaw or that the pivot point should be, moved farther to the left, it is only necessary to rotate the block 18 and. shift it to the right, as shown in Fig. 7. The pivot point now has been moved from point Aio point B, the new intersection or the axes of the springs H and i2. This has been accomplished without, in any material manner, shifting-thelclaw laterally, inasmuch as the block [1 .remains in a fixed position. Similar results could also be obtained by using, instead of the. springs, rigid links, the

ends. of which would be pivoted on the blocks l1. and i8 and at the points onthe arm 5 at which the springs are shown attached. The statementthat the springs prevent all points other end is attached. to the arm 5, as in Figs. 6 and '7, thereby fixing the lateral location of the claw with respect to the sprocket holes. In this modification,a clamping device consisting of a horizontally adjustable plate 22 is provided, on which there is a' rounded projection 23 contacting the upper surface of the spring H and a resilient block 24 of rubber or similar material directly under the projection 23. The block 22 is held to the supporting frame 25 by a pair of screws or bolts 26 'in'elongated slots in the block 22. The rubber block'24 serves'to resist any tendency of the spring to leave its pivot point on the projection 23 and also to damp any vibrations of the spring H which might tend to produce noise. The point o'fcontact between the projection 23 and spring H now" determines the pivot point for the arm 5, and this point may be shifted horizontally by moving the block 22 in the slots without'shifting the claw or the arm laterally. i

A preferred embodiment of the invention is illustrated in Figs. '1 to 5. The same principle is, applied, as'shown in Fig. 8, a horizontal fiat spring ser'ving to position the arm, while the pivot consists of 'a rocker point which can be shifted horiz'ontallyto adjust throw. -I-Iowever, the embodiment in Figs. 1 to 5 clifiers from that in Fig. 8, inthat the rocker point bears against the rigid portion'of the arm, instead of against the horizontal spring at a point intermediate said rigid portion and the mounting block [1, as in Fig. 8.

Referring now to the drawings of Figs. 1 to 5, in which the same'j numerals identify like elements, a pull-down arm 30 corresponds to the arm 5 in Figs. 61 '7, and 8, the arm 3!) having a claw element 3! attached thereto, the latter having' pull-down pins or'teeth' 32. A film 3d, with a singlerow of sprocket holes 35, is shown in Fig. l and Fig.' 2, in relation to the other elements of I the mechanism. The arm 38 has its follower portionv 3G in contact with a cam 38, drivenby sh'a ft39, shaft 39 having an inand-out cam do also mounted thereon to cause the teeth to enter the perforations 35 and be withdrawn therefrom, The cam 40 has its follower 4L attached to the arm 30, the follower 41 being held in contact with the surface of the cam 40 by :a compression spring 43 having one end fixedly'positionedby a bracket M attached to the frame 45 in anysuitable manner, such as by screws 46. (See Figs. 1 and 5.). Thus. as theshaft-39 is rotated, the cam All is rotated and the teeth 32 pass into and out of the sprocket holes 35 according to its up-and-down position tween the two prongs 5| of a fbr-k 50 and held against a rounded pivot edge '49 of the yoke of the fork by a spring 62. Mounted along the upper edge of the widened end of thearm .30 is .a hat spring .53 having one end bent over the end' of the arm and attached thereto by a screw 54 and its other end extending, and attached to, a lateral placement adjusting block 55 by a screw 56. The block 55 has a horizontal slot 58 therein and is, therefore, adjustable laterally and then firmly held in position by a pair of screws 59. Thus, any adjustment of the block 55 will control the lateral or horizontal position of the teeth 32 on claw 3| with respect to the sprocket holes 35 of the film 34, and once this adjustment has been made, it will maintain the lateral placement of the claw even though other adjustments are made to alter the amount of the up-and-do'wn travel of the -claw or the framing position of the claw. It will be noted that the spring 53 corresponds to the spring H in Figs. 6, '7, and 8, but extends in the opposite direction; namely, from its point of attachment to the arm to an anchor block on the right instead of on the left. This does not involv any difference in principle, but enables the spring to perform its function with less flexure. A spring Bl corresponding to spring 20 maintains follower 31 in contact with cam 38. The placing of spring 53 between the rocker edge 49 and body of arm 30 vhas no functional significance, but makes for convenience in attaching it to the body. It will be noted that the fork 50,

5| is deep and the body 30 is wide at this point.

cam 10. This arrangement permits framing of the picture in the aperture, inasmuch as it will shift the pivot edge of the fork 5D in a vertical direction only, thus changing the position that each picture frame is stopped at the end of the pull-down portion ofv the cycle, without shifting the arm 30 laterally, and without changing the amount of throw of the claw.

As mentioned above, it is also desirable to shift the throw of the teeth 32 without disturbing the lateral placement of the teeth of the claw with respect to the sprocket holes of the film. This is accomplished by laterally shifting the pivot edge of the fork without laterally shifting the arm itself according to the principle explained in connection withFig. 8. To make it.possible to shift the fork50 laterally, the bar (it is mounted to the frame 45 on screws 15 which pass throughhorizontally elongated holes in'the frame. The screws 15 pass through a backing member 16 to increase the holding ability to the adjustment when the fork 50 is once positioned. By shifting the pivot edge of the fork 50 along the spring 53, a longer or shorter throw is obtained for the claw without shifting it laterally, its lateral position being determined by the position of the block 55. A damper of any suitable material, such as a rubber block 51, is provided near the ends of the prongs 5| and bearing against a bracket (not shown) mounted on the frame ment,--.si;nce spring 16-] holds the arm against the rocker, but it "may be employed either as a substitute .for said :spring or supplementary thereto. It has the merit of reducing certain vibrations, :and thus, making the machine operate more :quietly. 1

While we prefer .to lemploy'a horizontal, flat spring, such as .53, to position the claw arm, there are other expedients for accomplishing the same purpose, which we regard as equivalent. For example, :a block corresponding to 55 and adapted to being shifted position, may carry a pin, engaging a vertical slot in arm 30,-or vice versa, the pin may :be on the arm and the slot in'the block. I v

It :is evident that the useful-features of the pivot system 'of our invention do not depend on making the blockiadjustablexinposition. If, for

of our invention is :in that the throw may be ad-,

justed'without disturbing theposition of the arm.

To obtain the type of downward motion during the pull-down portion of the cycle, as described a'b'cve, the cam 8 is providedwith a configuration such that, 'during its travel through the angle C, ca .slig-ht preliminary movement is obtained before the rapid pull-down motion which exists during rotation of the cam 38 through the angle D. (See Fig. .3.) At the end of angle D, a slower downward movement occurs through the angle E, after which a slight upward movement is given to the teeth 32 through the angle F at which point the claw is removed from the film by the cam 40. The preliminary downward motion brings the teeth 32 in contact with the film before the rapid motion begins, thus preventing a blow being imparted to the edges of the film perforations, which would occur if the claw should attain any considerable velocity before the teeth touch the edges of the perforations.

Since the friction of the film under the gate shoes is variable, and the end of the downward stroke is characterized by very rapid deceleration, there is the possibility of whipping of the end of the claw, leaving the actual stopping place of the film somewhat uncertain. A slight additional movement of the claw of the order of .001 to .002 inch, taking place more slowly and accompanied by smaller values of retardation, tends to make the final film position correspond more precisely with the geometry of the mechanism undisturbed by inertia effects. This small after movement, even though it be permitted to occur after the shutter has begun toopen, does not give rise to objectionable travel ghost since its magnitude is extremely small, and the interval of illumination of the screen while this small movement is'taking place, is a small fractionv of the cycle. After the teeth have reached their extreme downward posi 7 8 44, during half of which there is highdownward TABLE-Continued acceleration, and high retardation during the second half. The barn design is specified in terms m A 1 Travel 1 of the position the claw is to occupy,correspondagrees 9, 2 9 ing to each position'of the driving camp The Cam mus/deg: mus/deg mus method of layin outa cam when the desired fol-- 4 12' 19 lower position for each cam pcsitionis' given, is 1 .524 D well-known, and is illustrated for example, in 5 524 -55 D Figure 1 of the paper entitled Calculation of .-Ac 9 4.14 19. 43 celerations in Cam-Operated Pull-Down Mech- 10 7 .524 4-67 23-84 D anisms, by E. W. Kellogg, Journal .of the Society .524 D of Motion Picture Engineers, August 1945. In 8 524 5419 D the case of the present design, the pitch of the 9 5.72 34. 22 film perforations is taken as 300 mils for fresh 1O 6.24 4020 D film, but may be of any value between 300 and 15 .524 D about 29'? mils (0.297 inch) for films of various n 524 D degrees of shrinkage. The total throw-is seen to 12- 7.29 53.73 be 303.02 mils, so the teeth will enter the perfora- 13 181 6128 D tion of an unshrunk film with aclearance of about .524 D 3 mils. They then descend foriabout mils with M 524 D a velocity not exceeding 1 mil per degree of cam 15 8.86 77.95 rotation. Thus, with :films having perforation Y 16 .524 M8 87-07 D pitches of 299 to 300 mil pitch," the tooth velocity .524 D at the instant of contact will not exceed limil 524 9M2 D per degree. With films of greater Shrinkage, the 1s 10.43 105.29 teeth will reach slightly higher velocities before 10,96 1mg D making contact. If the film happens'to have a .524 D pitch of 297 mils (corresponding to one percent 20 524 D shrinkage), the velocity with which the teeth hit 21 12.00 140. 54 the edges of the perforations will be 1.75 mils per 30. 12. 53 15281 D degree. For comparison, we may consider a -.524 D dam of the usual type in which the acceleration 23 524 1200 165") D starts at full value and the totaltravel of 303 24 11-48 176,82 mils is to be achieved in 46 of cam rotation. 25 10% 138113, D This would call for an acceleration of 5.93 mils D per degree squared, and the velocity aft-er a travel 26 5% .1043 73 D of 3 mils, or at the point at which it would start 27 991 208-90 an unshrunk film, would be 1.855 mils per degree, 23 524 9, 38 213 D and at the end of a travel of 6 mils, where it n would strike a 1 percent shrunk film, the velocity 524 22167 D would be 2.62 mils per degree. Since the force of 30 an impact varies as the square of the velocity, 31 131 244,34 D the hammering of the teeth on the filmat the q D start of pull-down is very materially reduced by 524 D the employment of the principle of our invention 33 1 D just described. 34 0.24 255. 42

In the table, in order to conveniently calculate 1 velocities andaccelerations, time has been ex- 1524 V I 3? D pressed in units corresponding to one degree, of 36 524 2 D rotation of the driving cam. The velocities and 37 4.67 281.78 accelerations so expressed can be readily con- 38 286 13 D verted to standard units such as centimeters and 524 D seconds by application of Well-known dimensional 39 524 D formulas. Y 40 s. 10 29s. 42

TABLE 41 524 2. 57 295. 26 D 42 h 524 2. 05 29s. 57 D 524 D Propenzesof com 43 1.52 300.35 D 44- 1.0 301.52 Time A5551. Veloc. Travel 45 5 5 s02. 37 E Degrees a, v, 5, Angle 3 E Cam Rot. mils/deg. mils/deg. mils 46 .2 302. 72

v 47 0 2 s02 92 E 5 .5 O 0 0 4s 0 303 02 E 4 .5 25 F 3 .5 L0 1.0 c 49 5 -.5 302. 77 F 0 1 U 2 0 C 50 -1.0 302.02 F 1 0 a J 1 0 0 51 4 -1.5 500.77 F 0 1 0 4' 0 o 52 5 1. 0 299. 52 F 1 .524 1 52 5 26 D 53 7 5 -.5 298.77 F 2 .524 D 54 0 29s. 52 F n .524 D 55 298.52 5 2.57 9.35

this occurs whilethe-cam rotates through. angle F), and then' the teeth are" withdrawn under-the control of cam 40. Aside from more consistent positioning of the film, an additional advantage of ending the claw movement under conditions of low deceleration rate, is that lighter picture gate friction suffices to hold the film from overshooting the position to which the teeth push it.

It is not new in the motion picture art, to employ pull-down mechanisms in which the initial and final accelerations are less than the maximum values. For example, this is true of the familiar Geneva movement; but, this is an accidental characteristic, inherent in the mechanism, and takes the form of extremely high accelerations near the middle of the stroke, rather than very low accelerations at the beginning and end. In the cam ofour invention, the accelerations are applied in purposeful manner to (1) take up the slack at the beginning of the stroke without shock in spite of ordinary variations in the amount of slack, and as soon as this is done, (2) accomplish the main pull-down movement ina given time with the lowest compatible maximum values of acceleration and retardation (which is by immediately applying the chosen maximum value of acceleration and maintaining this to the middle of the stroke, and then applying an equal constant retardation for the balance of the principal movement), and (3) to push the film to its final position under conditions of very small rates of retardation, which must be low for a long enough period for the elements of the mechanism to recover from any vibratory disturbances resulting from the previous high retardation forces.

Thus, the above mentioned pull-down mechanism has the advantage of having an independent placement adjustment such as adjustable block 55, an independent throw adjustment, such as adjustable bar 64 which does not in any way disturb the lateral placement of the claw, and an independent framing adjustment, such as cam 10,

which in no way disturbs either the amount of the throw or the lateral placement of the claw. Furthermore, the pull-down motion has been im proved as stated above to provide a rapid action with accurate placement of the frame in the aperture with light gate tension and minimum wear on the film.

-We claim:

1. The method of intermittently advancing the frames of a motion picture film into and out of a projection aperture by a claw which comprises advancing said claw at a constant speed for a short-initial distance substantially one percent of the entire distance of advancement to contact said film, rapidly accelerating the advancement of said claw to advance said film for a distance substantially one-half that of the height of a picture frame, then advancing said claw and film over substantially the other half of said frame with substantially an equal negative acceleration, and thereafter advancing said claw and film at a propelling device I .a picture iframev one; motion picture film; requiring. a); movement of substan- .tially 298 mils into. a. projection: aperture: which comprises; imparting-to said? propelling-"device a slow' forwardimovementsat substantiallyzero. ac-

celer'ation, over as distance of substantially .5 mils, then: a substantially constant, .andiinel'atively 1 large positive .zaccelerationiEoveri'laldistancei of substantially 147- mils; then.- a; substantially constant, relatively large negative acceleration over a distance of substantially 147 mils, and finally a slow, forward movement with decreasing acceleration over a distance of substantially one mil, one-half mil of which has zero acceleration.

3. The method of cyclically advancing motion picture frames into and out of a projection aperture which comprises advancing said frames at a slow constant velocity over a small distance of the order of one percent of their total movement, applying to said frames a high acceleration over substantially one-half the distance of their total movement, decelerating said frames at a substantially equally high rate over substantially the remaining distance of their total movement, and continuing the movement of said frames at a decreased rate over substantially one-half percent of the distance of their total movement, a portion of said last movement being at a, constant velocity and at zero acceleration.

4. The method of claim 3, in which the total movement of said frames in any one cycle is substantially 298 mils, and said first slow constant velocity extends over a distance of from approximately 2 to 5 mils.

5. The method of claim 3, in which the period of said high acceleration extends over a distance of approximately 147 mils.

6. The method of claim 3, in which said period of high deceleration extends over a distance of approximately 14'? mils.

7. The method of claim 3, in which said decreased rate of deceleration extends over a distance of approximately one mil and said zero rate of acceleration extends over a distance of one-half mil.

8. The method of advancing the frames of a motion picture film into and out of a projection aperture, with the aid of a propelling device, which comprises causing said propelling device to intermittently engage the film, and imparting to saidpropelling device a movement characterized by a, slight initial acceleration period at the beginning of the advancement of said film, brief period of substantially constant velocity at zero acceleration following the slight initial acceleration, a period of positive acceleration, a substantially equal period of negative acceleration, and a brief period of substantially constant velocity at zero acceleration following the period of negative acceleration.

9. The method of claim 8, wherein the constant velocity at the beginning of the movement is maintained for a distance equal to approximately one percent of the entire movement.

10. The method of claim 8, wherein the period of substantially constant velocity and zero acceleration at the end of the movement corresponds to a movement of substantially one-half mil.

11. The method of claim 8, wherein the period of advancement of said propelling device is followed by a reversed movement thereof of sub:

stantially one-half percent of the entire movement, followed by disengagement of said propelling device.

12. The method in accordance with claim 1, in which said claw is finally moved in the reverse direction for a short distance at a substantially constant acceleration before movement of said claw substantially perpendicularly to said film.

13. The method in accordance with claim 2, in which said propelling device is finally moved in the reverse direction for a short distance at a substantially constant acceleration before move- 1 1.2 ment thereof substantiallyperpendicularly to its direction of advancement.

- EDWARD W. KELLOGG.

WARREN R. ISO-M.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 1 Name Date 1,900,876 Wittel Mar. '7, 1935 2,117,806 Holmes May 17, 1938 

